The sweepback of aircraft airfoils, or inclination of these airfoils in the flight direction, is a design feature of aircraft that fly at speeds approaching the speed of sound, and it is motivated by aerodynamic considerations. The aerodynamic advantage of the sweepback is that the adverse effects of compressibility, caused by the overspeed of the flow over the aerodynamic profile, which grow as the relative thickness of that profile increases, are related to the component of the airflow velocity that is essentially perpendicular to the line of 25% of the chord of the airfoil of the aircraft. Therefore, for a given flight speed, an airfoil with a given sweep angle will be subject to compressibility effects equal to those of an airfoil without sweepback but with an aerodynamic profile of a relative thickness equal to the cosine of the sweep angle. A greater relative profile thickness, defined as the ratio between the maximum thickness of the profile and its length in the flight or chord direction, results in a lower structural weight of the airfoil because the forces on the airfoil skins caused by aerodynamic loads are decreased. However, in the flight at high speed that is characteristic of large modern commercial aircraft, airfoils with large relative thicknesses of the aerodynamic profiles magnify the adverse effects of air compressibility, which can be manifested as shock waves on the airfoil, with an associated increase of the aerodynamic drag and other adverse flight phenomena. Therefore, the sweepback of airfoils serves to achieve a design balance between their structural weight and acceptable in-flight performance at speeds approaching the speed of sound.
The first airplane built for high speed flight with a significant sweep angle was the Junkers 287 in 1945. Among other unique characteristics of this aircraft, the sweep angle of the wings is negative, i.e., the wing tips are moved forward in the flight direction with respect to the root, or connection of the wings to the fuselage. Barring very few exceptions, such as the MBB/HFB 320, the Grumman X-29 and the Sukhoi 47 (all with negative sweepback wings), the immense majority of high speed aircraft are built with positive sweepback wings. Despite certain aerodynamic advantages of the negative sweepback, the fundamental reason for using a positive sweepback in the wings is that, in the event that the aircraft encounters a vertical air speed disturbance or gust during flight, the bending deformation of a wing with positive sweepback tends to decrease the local angle of attack of the wing profiles, which naturally mitigates the aerodynamic loads. In the case of a wing with negative sweepback, the effect is the opposite because, upon encountering a vertical gust, the bending of the wing causes increased angles of attack of the profiles that tend to increase the loads and bending. This means that the wings with negative sweepback tend to withstand significantly higher gust loads than positive sweepback wings and, therefore, they are heavier.
The aerodynamic advantages associated with an airfoil configuration with negative sweepback are well known and documented in the technical aeronautical literature. These advantages can be summarized as follows:                a smaller sweep angle of the leading edge of an airfoil with negative sweepback compared to an airfoil with positive sweepback, both for the same sweep angle of the line of 25% of the chord, results in less of a tendency for the aerodynamic flow to move along the direction of the wingspan, with a resulting reduction of the coefficient of friction in the boundary layer and, therefore, less aerodynamic resistance;        the air movement in the direction of the wingspan is from tip to root in the case of an airfoil with negative sweepback, which results in the possibility of achieving larger angles of stall of aerodynamic lift than in the case of positive sweepback airfoils, in which the transversal airflow in the wingspan direction drags the boundary layer towards the marginal tip or edge, decreasing the energy of the boundary layer in that zone which, as it has a higher local lift coefficient than the root zone, causes separation of the boundary layer with the resulting lift stalling at a smaller angle of attack than in the case of the negative sweepback airfoil; whereas a larger angle of stall of a horizontal stabilizer surface with negative sweepback makes it possible to increase the maximum aerodynamic force for a given surface or else reduce the surface and, therefore, the aerodynamic weight and resistance of that airfoil for the same maximum aerodynamic force, if this is the critical design consideration;        the elastic deformation of the airfoil under aerodynamic load, or aeroelastic deformation, tends to reduce the local angles of attack of the profiles in the case in which the surface has a positive sweepback, and to increase them if the surface has a negative sweepback, with the resulting increase in the aerodynamic lift gradient with the angle of attack in the case of a negative sweepback airfoil; this increase of the lift gradient increases the manoeuvrability of an aircraft with negative sweepback wing, which could be beneficial in the case of a military combat airplane but is usually considered as a drawback for commercial airplanes because the airplane's response sensitivity to vertical gusts is associated with the lift gradient, with which the internal loads and the weight of the wing structure also increase, and this is the main reason that explains the fact that negative sweepback wings are rarely used in commercial aviation (the abovementioned increase of the lift gradient due to the aeroelastic deformation associated with a negative sweepback surface is, however, advisable in the case of a stabilizer surface, since it enables reaching the aerodynamic force value required for the stabilizing function for lower angle of attack values of that surface).        
Despite the known aerodynamic advantages mentioned above, negative sweepback wings have associated structural performance complications that have limited their use in the design of airplanes; these can be summarized as follows:                The aeroelastic deformation tends to increase the structural loads and, therefore, the weight of the airfoil, and specifically the wing; moreover, the increased lift gradient of the wing results in a more dynamic response of the airplane to turbulence and to vertical gusts and, therefore, in less comfort for the passengers. However, in the case of a horizontal stabilizing surface of negative sweepback, this greater aerodynamic response to disturbances makes the stabilizer surface more efficient in its function of recovering the position of the airplane in the event that it encounters turbulence or vertical gusts during the flight and, therefore, it is a desirable effect, unlike in the case of the wings.        The geometry of the negative sweepback wing complicates the integration of the landing gear into a low wing commercial airplane because the rear spar forms an angle of more than 90 degrees with the rear of the fuselage, a consideration that does not apply to stabilizer surfaces.        Because of the larger sweep angle of the trailing edge, the flap type high lift systems lose aerodynamic efficiency; this consideration also does not apply to the stabilizer surfaces.        
The known drawbacks described above occur specifically in the wings but not on the stabilizer surfaces and, therefore, a horizontal stabilizer surface of negative sweepback would be more efficient (in terms of size, weight and aerodynamic drag) than a horizontal stabilizer surface of positive sweepback, if both stabilizer surfaces have their aerodynamic centre at the same distance from the aerodynamic centre of the wing, where the aerodynamic centre is the characteristic point of a lift or stabilizer surface for purposes of stability and control calculations.
However, there is no known use of horizontal stabilizer surfaces with negative sweepback in airplanes for high speed flight, including those mentioned above with negative sweepback wings.